How to get a vector type from a FloatVectorProperty?
Incorrect usage.

Property Definitions (bpy.props)
This module defines properties to extend Blender’s internal data. The
result of these functions is used to assign properties to classes
registered with Blender and can’t be used directly.

In python can set up a property on some class Foo with
Foo.prop = property(getter, setter)

the property definitions module is doing much the same for blender classes, with added goodies for UI etc.
&gt;&gt;&gt; bpy.types.Scene.prop_vector = bpy.props.FloatVectorProperty(default=(1,2,3))
&gt;&gt;&gt; C.scene.prop_vector[:]
(1.0, 2.0, 3.0)

Notice it is a tuple the size of the vector property (default 3).  To make it of vector type
v = Vector(C.scene.prop_vector)


Also consider to set the subtype of the FloatVectorProperty to eg. Direction to get &lt;class 'Vector'&gt; out of the box.  DIRECTION will typecast it to a vector but assign it no units.  For a translation use 'TRANSLATION` to put the lengths in chosen scene units (eg millimeters, inches).  See also the unit property
Generic XYZ vector
&gt;&gt;&gt; bpy.types.Scene.foo = bpy.props.FloatVectorProperty(subtype='XYZ')
&gt;&gt;&gt; C.scene.foo
Vector((0.0, 0.0, 0.0))

Following demo is based on operator_simple.py template:
import bpy
import mathutils
    
class SimpleOperator(bpy.types.Operator):
    &quot;&quot;&quot;Tooltip&quot;&quot;&quot;
    bl_idname = &quot;object.simple_operator&quot;
    bl_label = &quot;Simple Object Operator&quot;

    def execute(self, context):
        # Print type to console
        print (type(context.scene.my_vector))
        # Vector addition demo
        print(context.scene.my_vector + mathutils.Vector((1, 2, 3)))
        return {'FINISHED'}

def register():
    bpy.utils.register_class(SimpleOperator)
    bpy.types.Scene.my_vector = bpy.props.FloatVectorProperty(
            default=(1, 1, 1), 
            subtype='DIRECTION')

def unregister():
    bpy.utils.unregister_class(SimpleOperator)

if __name__ == &quot;__main__&quot;:
    register()

    # test call
    bpy.ops.object.simple_operator()